Is this a sponge?

[jeffmuse]

I have had this strange coral growing in the tank over the past few months... the thing grows approx. 2 inches per month. It is a white/clear color with a odd consistency.

I went ahead and pulled it out of the tank and I was surprised just how much of it there was growing behind the rocks. Here are some pictures, I assume it is a weird sponge of some kind?

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[fancyfish]

yes that looks like sponge

 

[jennm]

Yep that's what it is. Sometimes that sort is black too.

Jenn

 

[hammcd]

sponges r so cool...maybe cause u cant readily get them and they just sorta show up

 

[basscyn]

Yep.
I've got them to. I have white, yellow and black ones.
They like the shade